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Old 01-06-2013, 02:12 PM   #1
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Join Date: Dec 2012
Location: Battle Creek Mi
Posts: 25
My Ride: 2004 330i 6M OBM
No heat after expansion tank replacement

My expansion tank blew out on new years eve. Luckley I was able to make it home before temp got up to the 3/4 mark on temp gauge. Anyway I was planning to replace the cooling system this spring since I am new to this car per mangos thread. Being that it happend right after xmas I was only able to afford replaceing the minimum to get back on the road.
I purchased a new tank and a gallon of bmw antifreeze from the dealer. I replaced tank then filled system with 50/50 mix of antifreeze and distilled water and bled as described in mangos thread. All seemed good at first but now I am only getting heat for a few min after engine warms up then it goes cold. While hot if I remove the tank cap it relieves the pressure and heat is fine until the motor cools off then the same thing happens on the next warm up cycle. The upper and lower hoses are as hard as a bike tire until I open the cap to relieve pressure. The level of the coolant is in the middle of the high low mark when cold. I has been so for the last few warm up cycles. When I take off cap while hot I hear air esacape then if I squesse rad hose the put cap back on I can hear air go back into tank but then if a squese the hose with cap on no air comes back out.

My question is can the tank cap be causing an over pressureizing of the system not allowing the coolant to pass thru heat circuit? or possible bad HCV? Waterpump?

The heat worked fine before the tank let go. It was slow to put heat into the cabin until the engine was up to operating temp but work great after that.

I am a marine service teck with over 20 years exp so I know my way around and engine but not an expert on closed cooling systems as we dont use them often on inland lakes.

I plan to purchase a new cap for the tank in the new few days to see if that fixes the problem but I wanted to see if anyone has seen this before.

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